This invention relates to rubber articles having improved slip coatings and to methods of providing same. More particularly, the invention relates to rubber articles, such as sterile surgeons' gloves, which are provided with an improved slip coating. Still more particularly, the invention relates to such articles and methods wherein the slip coating is a non-elastomeric synthetic resin layer which when applied to the rubber substrate takes on the elastomeric characteristics of the rubber substrate.
It has previously been proposed to provide slip finishes on rubber articles such as rubber gloves or girdles by various methods. For example, the surface of a rubber glove can be halogenated with bromine or chlorine to make it slippery. However, this treatment may result in very poor aging properties. Discoloration can begin almost immediately and, within a month, the halogenated surface may become hard and brittle and brown in color. This can be avoided only by taking great care in the halogenation process and even then there is no assurance of obtaining a uniform, sustained, slip film. Waxes and silicones have been used but these provide only a temporary solution as these materials rub off in a very short time. It has further been proposed in U.S. Pat. No. 3,286,011 issued Mar. 18, 1964, and U.S. Pat. No. 3,411,982 issued Mar. 18, 1964, to provide a slip finish comprising a rubber latex and a resin latex. While such coatings reduce the coefficient of friction of the rubber article to a slight extent, it is desirable to further reduce the coefficient of friction. For example, it is desirable to further reduce the coefficient of friction to make it easier to put on and take off a rubber article such as a rubber glove.
In our co-pending application Ser. No. 220,692, we have disclosed an excellent resin slip finish for rubber articles. The resin used is a vinyl chloride-alkyl acrylate copolymer or a vinylidene chloride-alkyl acrylate copolymer. While the slip finish is excellent, it may produce a "cobblestoning" effect when the rubber article is stretched to a large extent, of for example, over 450 percent. In surgeons' gloves, for example, stretchability of 700 percent is desired. Where gloves in accordance with our earlier invention are stretched to that extent, they tend to cobblestone, a condition which is not desirable in use.
Also, in the preparation of rubber articles by dipping a form into a rubber latex followed by coagulation of the rubber latex into the desired article, it has heretofore been necessary to first apply to the form a coating of a release agent such as a mold release powder, e.g. talc, diatomaceous earth, etc. or a lubricant type release agent, e.g. glycerine. The reasons for the use of the release agents are (1) to prevent damage to the rubber article when it is stripped from the form and/or (2) to preclude the tendency of the tacky rubber to self adhesion when the article is removed. Use of release agents in the preparation of dipped rubber articles, however, is not without its shortcomings for it naturally leads to adulterated final products which have trapped or otherwise picked up the release agent on the coagulated rubber surface. Nevertheless, the contaminated rubber article is a matter which manufacturers of such articles have had to live with for it has not been possible to obtain these rubber articles in a commercially acceptable form without the use of the release agents.
Another shortcoming commonly associated with the use of release agents in the manufacture of rubber articles is that the process requires clean up of the residue of the release agent on the mold or form after formation of each and every article, a tedious and time-consuming operation.
The same problems necessitating the use of release agents in the formation of rubber articles directly on dipping forms, likewise necessitate the use of release agents in processes such as described in U.S. Pat. No. 3,411,982 to Kavalir et al., wherein the slip-coated rubber articles are prepared by first providing a release composition onto the form before it is dipped into the rubber latex. In addition to the aforementioned stripping and self-adhesion difficulties, there is a tendency for the slip coating to separate from the rubber substrate when release agents are not utilized in such processes.
Furthermore, in the prior art processes for obtaining slip coatings there has been a tendency for the surface of the articles produced to exhibit streaks.
Thus, it is the object of the invention to provide rubber articles containing slip coatings on at least one surface thereof which slip coatings are comprised of non-elastomeric materials which when applied to the rubber substrate take on the elastomeric properties of the rubber substrate.
It is also an object of the invention to provide non-elastomeric slip coated rubber substrates which can be stretched a very large amount without separation of the rubber and slip coat phases.
Yet another object of the invention is to provide a process for the production of rubber articles which process does not require the use of release agents as a separate and distinct entity and which nevertheless results in a rubber article having a slip coating which has an appreciably lower coefficient of friction than the rubber surface to which it has been applied.
A further object of the invention is to provide a process for obtaining slip coatings on rubber articles characterized by being free of streaking.